Answer with explanation:
 Speed
 

When you will observe the graph
Time is represented on X axis
And , Distance traveled is represented on Y axis.
In 5 hours ,Henry travels a distance of 300 miles.
So, in 1 hour distance traveled by Henry 
 
 miles
 miles
So, Speed of Henry
 

Speed can be calculated by this method also
 

Option D: 60 miles per hour